Voltage regulation



Patented Feb. 10, 1948 VOLTAGE REGULATION William H. Bixby, Detroit,Mlch., assignor to Donald R. Middleton and Stanley M. Hanley, doingbusiness as Power Equip Micln, a copartnership Application January 31,1945, Serial No. 575,463

Claims. (Cl. 32 -89) This invention relates to voltage regulation anmoreparticularly to apparatus for controlling the current supplied froman alternating current source to a load to minimize load voltagechanges.

An object of the invention is to provide novel apparatus for regulatingthe current supplied from an alternating current source to a load tominimize load voltage changes.

Another object is to provide novel apparatus for regulating the currentsupplied from an alternating current source to a load to maintain theload voltage substantially constant irrespective of changes of linevoltage and load current.

Another object is to provide a novel voltage regulating circuit which isrelatively insensitive to changes in frequency of the current suppliedto the load.

In accordance with a specific embodiment of the invention herein shownand described for the purpose of illustration, there is provided aregulating circuit comprising a reactor having a first winding on amagnetic core connected in series with an alternating current supplysource and a load. A second winding on the core of the reactor issupplied with unidirectional current from a rectifier for controllingthe impedance of the first winding and thereby controlling the currentsupplied from the alternating current source to the load.

The rectifier is provided with control means upon which is impressed forcontrolling the rectifier output current, an alternating voltage whichvaries in response to changes of load voltage and load current. Forsetting up the control voltage there is preferably provided a bridgecircuit having two parallel branches across which are impressed analternating voltage derived from and proportional to the load voltage.In one of the branches there are connected in series a resistor andresistance means comprising a device, preferably a thermistor, havingthe characteristic that its resistance decreases in response to anincrease of alternating current therethrough at such a rate that thevoltage thereacross decreases. The second branch comprises in series aresistor and the anode-cathode path of a space discharge device havingan anode, a cathode and a control electrode. This branch also hasconnected therein a load compounding resistor of relatively small ohmicvalue through which the load current fiows for setting up thereacross analternating voltage corresponding to load current. Three componentalternating voltages are set up in a circuit connecting the controlelectrode and cathode oi the space discharge device, namely, a firstment Company, Detroit,

voltage derived from and proportional to the load voltage, a secondvoltage set up across the resistance means comprising the thermistor anda third voltage proportional to load current set up across the loadcompounding resistor. The

age to control the current supplied from the rectifier to the saturatingwinding of the reactor to cause the load voltage to be maintained.substantially constant. The resistance means comprising the thermistormay consist solely of the thermistor or equivalent device or may have anadditional resistance element having the characteristic that, during thestarting period while the thermistor and additional resistance element.are heating, its resistance changes with time to act as athermalcompensating element to compensate for the fall of resistance with timein the thermistor. For a given current the resistance across thethermistor and thermal compensating resistor should remain constant withtime during the starting period.

However it is not necessary to employ, in a circuit branch supplied withcurrent from the load circuit, a' resistor of substantially constantresistance and a resistance means the voltage across which decreases asthe alternating current therethrough increases. the branch circuitcomprise a resistance device the resistance of which changes in aconsistent, non-linear manner with changing effective current in thecircuit, that is, the voltage across the device must not be proportionalto the current through the device. The only advantage to be gainedfrom.the use of a device the voltage across which decreases withincreasing current therethrough is to make possible the use of a voltageamplifying circuit of relatively smaller gain while maintaining the loadvoltage within certain desired limits. The use of a non-ohmic resistancedevice the voltage. across which increases with increasing currenttherethrough has other advantages and the use of such a device is,therefore. preferred in some cases. There are shown and described hereinseveral typical cir- It is only required that cuit arrangements, whichare modiiications of the arrangement described in the precedingparagraphs, for utilizing the sum of two alternating voltage componentswhich are opposed in phase. one of the components varying linearlywithioad voltage and the other component varying nonlinearly with loadvoltage, for obtaining a resultant control voltage. The control voltagemay he used for controlling the direct current supplied to the directcurrent winding of a reactor to control the impedance of the alternatingcurrent winding of the reactor to cause load voltage changes to beminimized.

Fig. l of the accompanying drawing is diagrammatic view of a voltageregulator embodying the invention;

Figs. 2 and 3 are diagrammatic views of modifications of a portion ofthe circuit arrangement of Fig. 1; and

Figs. 4 and 5 are graphs to which reference will be made in describingthe arrangements shown in Figs. 2 and 3.

Referring to Fig. 1 of the drawing. current from an alternating currentsource III is supplied through a line I2, I3 to a load II. In one sideof the line I2 there is connected a series load compounding resistor I4,and in the other side of the line I3 there is connected a winding I5 ofan inductive reactor comprising a threelegged core I6 of magneticmaterial, the winding l5 wound on the two outer legs and a winding I'Iwound on the middle leg. In some cases it may be desirable to omit theload compounding resistor I I and to directly connect one side of thesupply line I2 to a terminal of the load II. Current from source Ill.isalso supplied to the primary winding I8 of a transformer havingsecondary windings I9, 20 and 2|. The primary winding I8 is connectedacross the load II. The reluctance of the magnetic circuit for thewinding I5 and, therefore, the impedance of winding I5, is controlled bythe direct flux set up in each of the outer legs of the core in responseto rectified current supplied to the winding II. The rectifier forsupplying unidirectional current to winding I'I comprises electricdischarge tubes 25 and 26 each having an anode, a cathode and a controlelectrode, the control electrode of tube 25 being directly connected toits cathode. The cathodes of tubes 25 and 26 are connected to oneterminal of winding II. The end terminals of secondary transformerwinding I9 are connected to the anodes of tubes 25 and 26, respectively,and a mid-terminal of winding I9 is connected to the other terminal ofwinding II. A control voltage is set up and impressed upon the controlelectrode-cathode circuit of tube 25 to control the direct currentsupplied from the rectifier to the winding IT.

For setting up a voltage for controlling the rectifier 25, 28, there isprovided a bridge circurt having two parallel branches connected acrossthe secondary transformer winding 2|. One of the branches comprises inseries a resistor 30, the anode-cathode path of an electronic device 3|having an anode, a cathode and a control electrode, and the loadcompounding resistor I4 the resistance of which is small relative tothat of resistor 30 and relative to the anode-cathode resistance of tube3|. The other branch comprises a resistor 32, a thermistor 33 and athermal compensating resistor 34. The output of galvanometer corners ofthe bridge are connected to the control electrode and cathoderespectively of rectifier tube 25, the common terminal of resistor 32and thermistor 33 being one output terminal, and the common terminal ofresistor 33 and the anode oi tube 3i being the other output terminal.The thermistor is one having the characteristic that the resistancethereof varies at such a rate in response to amplitude changes of thecurrent therethrough over a certain current range, which includes theoperating range, that the voltage across the thermistor decreases as thecurrent increases and vice versa.

The thermistor 33 is somewhat sluggish in changing its resistance inresponse to current changes so that its resistance remains nearlyconstant over the period of a single cycle of alternating current fromsource I. which may have a frequency of 60 cycles per second, forexample. A path connecting the control grid and cathode of tube 3|includes three sources of alternating voltage in series, namely, a firstvoltage across the secondary transformer winding 20 which varies inaccordance with load voltage changes, a second voltage, that across thethermistor 33 and compensating resistor 34, which falls as the voltageacross the load rises, and a third voltage across load compoundingresistor I4 which varies in accordance with changes of load current. Thefirst component voltage is degrees out of phase with respect to each ofthe remaining component voltages and is of larger amplitude than the sumof the remaining component voltages. The resultant control gridcathodevoltage is therefore opposed in phase to the anode-cathode voltage, thatis, the control grid is negative with respect to the cathode when theanode is positive with respect to the cathode. During the half cycles ofthe alternating voltage when the anode of tube 3| is positive withrespect to its cathode, the anode of rectifier tube 25 is also positivewith respect to the cathode of that tube.

Considering the operation of the regulating circuit, suppose that asmall increase in load voltage occurs due to an increase of the voltageof the supply source III, for example. There will then be produced anincrease in the alternating voltage drop across resistor 32 due to thevoltage rise across secondary transformer winding 2|, the alternatingvoltage across the thermistor 33 and its compensating resistor 34decreasing. Due to the increase oi the alternating voltage acrosssecondary winding 20 in the control electrode-cathode circuit of tube3|, a relatively large decrease in peak voltage drop across resistor 30takes place during the positive half cycles of the anode-cathode voltageof tube 3|. During these positive half cycles, therefore, the potentialof the control electrode of tube 25 with respect to its cathode becomesrelatively less positive or more negative. The current supplied by therectifier to the reactor winding I1 is thus decreased to cause theimpedance of winding I5 to increase. As a result the current supplied tothe load II is decreased to tend to prevent the initially assumed risein load voltage. In case of failure of tube 3| the voltage drop acrossresistor 30 is reduced to zero and the control grid bias applied torectifier tube 25 is changed in a direction to reduce the rectifiercurrent supplied to winding II, thus causing a decrease in load voltage.When the load current is increased, due to a reduction of the loadresistance, for example, the voltage drop across load compoundingresistor I4 increases to make the control grid of tube 3| relativelymore positive or less neg- I aasa ra increased load. The inductance ofthe saturat- I ing winding I1 is sufiiciently large to provide efiectivefiltering of the output current from the rectifier, that is, it Jprevents rapid current changes therethrough. This action tends toequalize or balance the portions of the rectified current supplied bythe rectifier tubes 25 and 28, respectively.

In a specific regulator circuit of the type shown in the drawing anddescribed above tubes 25 and 26 were R. C. A. 2A3 triodes and tube 3|was an R. C. A. 6SF5 triode. The resistance values of resistors I4, 30,32 and 34 were respectively 0.435 ohm, 250,000 ohms, 4,000 ohms and 700ohms. The resistance of thermistor 33 was 1,765ohms. The winding I 5 ofthe reactor had 105 turns on each outer leg of the core and the windingI! on the middle leg had 10,000 turns. The core was made up of a 2% inchstack of No. 26 gauge, EI-19 Allegheny Transformer Company, A-grade,iron laminations interleaved. The windings of transformers l8, I9, 20,21 were such that when the load voltage acros primary winding l8 was 85volts, the voltage across each half of secondary winding l9 was 250volts, the voltage across secondary winding 20 was 52.6 volts and thevoltage across winding 2| was 170 volts. In a test made on thisregulating circuit, when the source l0 had a frequency of 60 cycles persecond and its voltage was varied over the range from 100 to 130 volts,the load voltage varied from 84.1 to 85.3 volts for a load of 1.0ampere, from 84.2 to 85 volts for a load of 2.0 amperes, and from 84.2to 85.0 volts for a load of 3.0 amperes. When the frequency of thevoltage source l0 was changed to 50 cycles per second and the testrepeated for the input voltage range 01' 100 to 130 volts, the loadvoltage varied from 84.9 to 86.1 volts, from 84.9 to 85.3volts and from84.7 to 85.2 volts for loads of 1.0, 2.0 and 3.0 amperes. respectively.For a range of input voltage from 100 to 180 volts and a frequency of 40cycles per secondpthe load voltages obtained varied from 84.7 to 86.9volts, from 84.6 to 86.0 voltsand from 84.1 to 85.9 volts for loads of1.0, 2.0 and 3.0 amperes, respectively. It will be observed that theload voltage is substantially constant irrespective of changes of linevoltage, load and frequency.

Where the load voltage is substantially equal to the voltage which isrequired to be impressed upon the circuit connected across secondarytransformer winding 2|, this transformer wind-. ing may be dispensedwith and the circuit which is connected to the transformer winding, as

changed by eliminating the secondary transformer winding 20 and the tube31, by substituting a resistor in the bridge circuit in place of theanode-cathode path of tube 3| and by adding a vacuum tube amplifier foramplifying the voltage at the output or galvanometer terminals of thebridge circuit and impressing the amplifier output voltage upon thecontrol grid-cathode circuit of tube 25. The cathode of the amplifiertube will be connected to the common terminal of the thermistor 33 andresistor 32' and the control grid of the amplifier tube will beconnected to the common terminal of resistor 30 and the resistor whichis connected inthe bridge circuit in place of the anode-cathode path oftube 3!. The load terminal which is connected to the reactor winding l5,as shown in the drawing, will be connected through an anode resistor tothe anode of the voltage amplifier. The common terminal of the anode andanode resistor will be connected to the control electrode of tube 25 andthe other terminal of the anode resistor will 'be connected to thecathodes of tubes 25 and 26.

Moreover, if desired, the amplifier in the above-described modificationmay be omitted and the bridge circuit transformer coupled to I nected tothe cathodes of tubes 25 and 26. The

resistance values of the bridge arms are so chosen that the alternatingvoltage across the primary winding of the coupling transformer, which isconnected to the output terminals of the bridge, increases when the loadvoltage increases, and vice versa, and the terminals of the primarywinding are so connected to the respective bridge output terminals thatthe control grid-cathode. voltage applied to each rectifier tube is inphase opposition to its anode-cathode voltage, that is, the control gridis'negative with respect to the cathode when the anode is positive withrespect to the cathode. In this arrangement it may be necessary toprovide a high turn 'ratio in the coupling transformer and someprovision may then be desirable to prevent excessive voltage in thesecondary under abnormal conditions of operation. I

The control circuit shown in Fig. 2 is a modification of a portion ofthe control circuit shown in Fig. 1, the corresponding circuit elementsbearing the same designations in the two figures. Current from a sourceI 0 is supplied to the load ll through the alternating current windingl5 of a reactor by way of the leads a, b, as shown in Fig. 1. Leads 0, dgo to the cathode and control electrode; respectively, of a rectifiertube 25, as shown in Fig. 1. The tube 3| is a pentode the screen grid ofwhich is connected to a tap of transformer winding 2|. Resistor 42 has afixed value of resistance and corresponds to the resistor 32 ofFig; 1.Resistor .43 has a negative temperature coemcient, its resistancedecreasing as the current through the branch 42, 43 increases. a

As shown in Fig. 4, the. voltage E20 across transformer winding 20varies linearly with load 7 voltage. The voltage E43 across resistor 43varies non-linearly with load voltage, the voltage E43 being nearlyconstant in the region of the normal operating load voltage 2:. The sumof voltage E20 and the voltage E43 is impressed upon the controlgrid-cathode circuit of tube 3|, these voltages being opposed in phaseand the voltage E28 being larger than the voltage E43. The phase of theresultant voltage is such that the control grid is negative with respectto the cathode when the anode is positive with respect to the cathode.This resultant voltage, e in Fig. 4, increases in response to anincrease of load voltage, and vice versa. When the load voltageincreases, for example, the anode current of tube 3| decreases to makethe potential of lead c going to the cathode of the rectifier tube 25relatively more positive with respect to lead d going to the controlgrid of tube 25. The rectified current supplied to the impedance controlwinding of the reactor, therefore, decreases to cause the reactance ofthe reactor winding l5 to increase,

thus tending to reduce the current supplied to the load. The assumedrise of load voltage, therefore, is minimized or substantiallyprevented.

In accordance with another embodiment of the invention, resistor 43 ofFig. 2 is a fixed resistor and resistor 42 is a resistor, a tungstenfilament lamp, for example, having a positive temperature coefiioient sothat the resistance of resistor 42 rises in response to an increase ofcurrent therethrough and vice versa. The curves of Fig. 4 also apply tothe circuit of Fig. 2 when thus modified. The current through resistor43 does not increase in proportion to an increase in load voltagebecause of the increasing resistance of resistor 42. The rate of changeof the voltage E43 across resistance element 43 with respect to loadvoltage, therefore, decreases as the load voltage is increased as shownby the curve in Fig. 4. The circuit of Fig. 2, therefore, functions inthe same manner when element 43 has a constant resistance and element 42has a resistance which increases with increase of current therethroughas it does when element 42 has a constant resistance and element 43 hasa resistance which decreases with increasing current therethrough.

The circuit of Fig. 2 may be further modified to cause the production ofa larger change in the control grid-cathode voltage e in response to achange of load voltage by employing a positive temperature coefiicientresistance element 42 the resistance of which increases in response toan increase of current flowing through it and a negative temperaturecoeihcient resistance element 43 the resistance of which decreases inresponse to an increase of eil'ective current therethrough. In thiscase, the decreasing resistance of element 43 will result in a furtherdecrease in the rate of increase of the voltage E43 with respect to theload voltage as the load voltage is in-v creased, or the voltage E43 mayeven decrease as the load voltage rises over the operating range.

The use of a positive temperature coeflicient resistor 42, such as atungsten filament lamp, in the circuit of Fig. 2 has the distinctadvantage that failure of the lamp element would result in a reductionof load voltage.

Fig. 3 is a further modification of the regulator circuit shown inFig. 1. Anode current is supplied to the tube 3| through anode resistor55 from the secondary transformer winding 54. A tap of transformerwinding 54 is connected to the screen grid of the tube. Secondarytransformer winding 55 supplies current to the resistor elements 52 and53 in series, the common terminal of windings 54 and 55 being connectedto the cathode. 20 is connected to the common terminal of resistors 52and 53 and its other terminal is connected to the control grid of tube3|. When the anode is positive with respect to the cathode of tube 3|,the terminal of resistance element 52 which is connected to the cathodeis positive with respect to its other terminal. The voltage acrossresistor 52 and that across the transformer winding 20 are opposed inphase in the control grid-cathode circuit of tube 3|, the voltage acrossthe resistor 52 being larger. Therefore, the control grid is negativewith respect to the cathode when the anode is positive with respect tothe cathode over the operating range of load voltage.

The voltage E20 across transformer winding 20 is a linear function ofthe voltage across the load H as shown in Fig. 5. The resistor element53 may have a constant value of resistance while the element 52 may havea positive temperature coefficient so that its resistance increases withincreasing eilective load voltage. The voltage E52 across resistor 52 isshown in Fig. 5 as being a nonlinear function of load voltage, that is,the rate of change of voltage E52 increases with increasing loadvoltage. The resultant voltage e in the control grid-cathode circuit oftube 3| increases with increasing load voltage, and vice versa, in theregion of the normal load voltage 1:. When the load voltage increases,for example, the control grid of tube 3| becomes relatively more nega--tive with respect to the cathode during the half cycles when the anodeof the tube is positive so that the anode current and the voltage dropacross anode resistor 56 decrease. The control grid of rectifier tube 25thus becomes relatively less positive with respect to the cathode ofthat tube to cause a reduction of the rectified current supplied to thereactor. The reactance of the reactor winding i5 is thus increased toreduce the load current. The initially assumed rise of load voltage isthus minimized or substantially prevented.

Instead of employing resistive elements 52 and 53 having thecharacteristics described above, resistor 52 may have a constant valueof resistance and resistor 53 may have a resistance which decreases withincreasing goat-meanssquare current therethrough. In this case,-when theload voltage rises, the resistance of element 53 decreases to cause therate of change of voltage E52 across element 52 to increase withincreasing load voltage as shown in Fig. 4.

As a further modification of Fig. 2, there may be employed a resistor 52having a positive temperature coefficient of resistance and a resistor53 having a negative temperature coefficient. In this case, the rate ofchange of voltage E52 will increase with increasing load voltage butthis increase is more rapid thanin the case where the resistor 52 has apositive temperature coefilcient and resistor 53 has a constant value ofresistance.

What is claimed is:

1. Regulating means for controlling the current supplied from analternating current source to a load for minimizing amplitude changes ofthe alternating load voltage comprising a reactor having a first windingconnected in series with said load and a second winding to which directOne terminal of transformer winding 5 of said first winding, resistancemeans to which current from said source is supplied to set up analternating voltage, said resistance means comprising a device theresistance of which changes in response to changes of eilective currentflowing therethrough, means to which current from said source issupplied for setting up a second alternating voltage the amplitude ofwhich varies due to voltage changes of said source, means for combiningsaid alternating voltages in opposed phase to set up a resultantvoltage, rectifying means for supplying direct current to the secondwinding of said reactor and control means responsive to said resultantalternating voltage for controlling the amplitude of said directcurrent, thereby controlling the impedance of the first winding of saidreactor to maintain said load voltage substantially constant.

2. Regulating means for controlling the current supplied from analternating current source to a load for minimizing amplitude changes ofthe alternating load voltage comprising a reactor having a first windingconnected in series with said load and a second winding to which directcurrent is supplied for controlling the impedance said first winding,resistance means to which current from said source is supplied to set upan alternating voltage, said resistance means comprising a device theresistance of which changes in response to amplitude changes of thealternating current flowing therethrough, means to which current fromsaid source is supplied for setting up a second alternating voltage theamplitude of which varies due to voltage changes of said source,electronic means having an anode, a cathode and a control electrode, acircuit connecting said control electrode and said cathode comprising aportion of said resistance means across which a first voltage is set upand said means for setting up said second alternating voltage, saidfirst and second voltages being opposed in phase, a circuit connectingsaid anode and said'cathode including means for deriving from saidalternating current source and impressing upon said last-mentionedcircuit a third voltage, a rectifier for supplying direct current to thesecond winding of said reactor, said recti fier having a control meansfor controlling said direct current in response to a voltage impressedthereon, and means for impressing upon said control means a voltagewhich varies in response to current variations in said anode-cathodecircuit.

3. Means for supplying current from an alternating current source to aload and for regulating the load voltage to tend to maintain it constantcomprising a reactor having a first \winding and a second winding eachwound on a common core of magnetic materiahmeans for connecting saidfirst winding in series with said load with respect to said source, arectifier for rectifying alternating current from said source and forsupplying the rectified current to said second winding, control meansfor said rectifier for controlling the rectified current supplied tosaid second winding and thereby correspondingly controlling theimpedance of said first winding in response to a control voltageimpressed upon said control means, a bridge circuit having its outputterminals connected to said control means for impressing a, controlvoltage upon said control means, said bridge circuit comprising twoparallel branches across which is setup an alternating voltage derivedfrom said source, an electronic device having an anode, a cathode and a7 control electrode and having its anode-cathode path in one of saidbranches and a circuit connecting said control electrode and saidcathode comprising in series means for setting up an alternating voltagederived from said alternating current source and ,having variationscorresponding to load voltage changes and means for setting up a secondalternating voltage derived from said alternating current source, saidlast-mentioned means comprising a device theresistance of which changesover the operating range as a function or the current flowingtherethrough, said alternating voltages being of opposite phase in saidcircuit.

4. Means for controlling the alternating current supplied to a load froman alternating current supply source comprising impedance means inseries with said load with respect to said source, means for controllingthe impedance of said impedance means in accordance with the directcurrent energization of said impedance'controi means, means forrectifying alternating current from said source and for supplying. therectified current to said impedance control means, said rectifying meanscomprising a first space discharge device having an anode, a cathode anda control electrodaa second space di charge device having an anode, acathode and a control electrode, a circuit connecting the anode andcathode of .said second space discharge device comprising a firstalternating voltage source derived from said alternating current supplysource and a resistor, a circuit connecting the control, electrode andcathode of said second space discharge device comprising a secondalternating voltage source derived from said supply source and havingvariations due to voltage changes thereof and a third alternatingvoltage source derived from said supply source, said third sourcecomprising a device the resistance of which changes over the operatingrange in response to amplitude changes of the alternating currentflowing therethrough, said second voltage being larger than said thirdvoltage and opposed in phase thereto, said first alternating voltagebeing opposed in phase to said second voltage so that the polarity ofthe control electrode of said second space discharge device is negativewith respect to its cathode during periods when its anode is po itivewith respect to its cathode, the resulting current set up in theanode-cathode circuit of said second space discharge device being apulsating current having variations due to voltage changes of saidsupply source and a circuit connecting the control electrode and cathodeof said first space discharge device comprising said resistor, therebycontrolling the rectified current supplied to said impedance controlmeans for minimizing changes of voltage across said load.

5. In combination with a load to which current is supplied from analternating current supply source the voltage of which may vary, ofreactance means having an alternating current winding connected inseries with said load with respect to said source and a direct currentwinding for controlling the impedance of said alternating currentwinding under control of direct current supplied to said directcurrentwinding, 9, first, a second and a third secondary source of alternatingcurrent derived from said supply source, the voltages of said secondarysources having variations due to voltage changes of said supply source,a circuit having two branches connected across said first secondarycurrent source, a first of said branches comprising in series a flrstresistor and the anode-cathode path of an electronic device having ananode, a cathode and a control electrode, a pulsating current from saidfirst secondary source being caused to fiow in said branch, the secondof said branches comprising in series a second and a third resistor theresistance of one of which, at least, changes in response to amplitudechanges of the eflective current flowing in said second branch to causeto be set up across said third resistor an alternating voltage whichvaries non-linearly with the voltage across said second branch, acircuit connecting the control electrode and cathode of said electronicdevice comprising in series said third resistor and said secondsecondary source of alternating current, the voltage across said secondsecondary source being opposed in phase to the voltage across said thirdresistor, means for rectiiying current from said third secondary sourceand for supplying the rectified current to said direct current winding,said rectifying means comprising control means upon which a voltage isimpressed for controlling the rectified current supplied to said directcurrent winding, and means for impressing upon said control means avoltage having variations correspondin to the amplitude variations ofthe pulsating current flowing in said first branch circuit including theanode-cathode path of said electronic device.

6. In combination with a load to which current is supplied from analternating current supply source the voltage of which may vary, ofreactance means having an alternating current winding conne ted inseries with said load with respect to said source and a direct currentwinding for controlling the impedance of said alternating currentwinding under control of direct current supplied to said direct currentwinding, a first, a second and a third secondary source of alternatingcurrent derived from said supply source, the voltages of said secondarysources having variations corresponding to load voltage changes, acircuit having two branches connected across said first secondarycurrent source, a first of said branches comprising in series a firstresistor and the anode-cathode path of an electronic device having ananode, a cathode and a control electrode, a pulsating current from saidfirst secondary source being caused to flow in said branch, the secondof said branches comprising in series a second and a third resistor theresistance of one of which, at least, changes in response to amplitudechanges of the alternating current flowing in said second branch, acircuit connecting the control electrode and cathode of said electronicdevice comprising in series one oi said second and third resistors andsaid second secondary source of alternating current, the voltage acrosssaid second secondary source bein opposed in phase to the voltageacrosssaid one of said second and third resistors, means for rectifyingcurrent from said third secondary source and for supplying the rectifiedcurrent to said direct current winding, said rectifying means comprisingcontrol means upon which a voltage is impressed for controlling therectified current supplied to said direct current winding, and a circuitincluding said first resistor and one of said second and third resistorsin series for impressing upon said control means a, control voltageequal to the sum of the voltages across the resistors, respectively, insaid control circuit.

7. A voltage regulator comprising means for connecting a source ofalternating voltage to a load to supply alternating voltage to saidload,

a unidirectionally conductive electronic spacecurrent device having ananode, a cathode and a current control electrode, an input circuit forsaid device terminating in said cathode and said control electrode,means under control 01 current from said source for introducing analternating voltage of the frequency or that of said source into saidinput circuit, means for introducing an alternating voltage derived fromsaid source into the anode-cathode circuit or said device, a resistancepath a portion of which is in said input circuit in series relation tosaid alternating voltage therein, said resistance path comprising aresistor the resistance of which changes in response to the temperaturechange produced by a change of the efiective current flowingtherethrough, which thermal action is too sluggish to be appreciableduring the period 01' a single cycle of the voltage or said source,means for causing alternating current derived from said source to flowthrough said resistance path, said last-mentioned current increasingwith any increase of said alternating voltage in said input circuit,whereby the change in voltage between said cathode and said controlelectrode is greater than the change in said alternating voltageintroduced in said input circuit and is dependent upon the change inroot mean square value of said current flowing through said resistancepath, and means under control of the current in said output-circuit forcontrolling the voltage supplied to the load.

8. Regulating apparatus in accordance with claim 7 in which saidlast-mentioned means comprises a rectifier having a current controlelectrode under control of the alternating current in said outputcircuit, said rectifier being supplied with current from saidalternating source, and a reactor having a, winding through whichcurrent to said load flows and a second winding supplied with currentfrom said rectifier.

9. A voltage regulator comprising means for connecting a source oialternating supply voltage to a load, a space discharge device having ananode, a cathode and a space-current control electrode, means forintroducing into a circuit connecting the anode and cathode 01 saiddevice an alternating voltage derived from said source, a current pathcomprising in series a first and a second resistance means, one of saidresistance means having a resistance-current characteristic such thatits resistance increases in response to a change in a certain direction01' the root mean square value of the current flowing in said currentpath, the other of said resistance means having a resistance-currentcharacteristic which difiers from that of said one of said resistancemeans, means for introducing into said current path an alternatingvoltage derived from said source, a circuit connecting the controlelectrode and cathode comprising said second resistance means, means forintroducing into said last-mentioned circuit an alternating voltageproportional to the voltage across said load in opposed phase to thevoltage across said second resistance means, and means under control ofthe current in said anodecathode circuit for controlling the voltagesupplied to the load.

10. A voltage regulator in accordance with claim 9 in which saidlast-mentioned means comprises a reactor having a first winding throughwhich current from said supply source flows to said load and a, secondwinding for controlling the impedance oi said first winding inaccordance with the amplitude of direct current supplied 13 thereto. a.rectifier for supplying direct current to said second winding and meansunder control of the current in said anode-cathode circuit forcontrolling said rectifier to control the amplitude of saiddirect'current. WILLIAM H; BIxBY.

I REFERENCES CITED The following references are of record in the file 01this patent:

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